Reducing the effect of signal interference in null areas caused by overlapping antenna patterns

ABSTRACT

A wireless communication system for transmitting and receiving wireless communications using at least one beam is disclosed. The system comprises a plurality of WTRUs, at least one beam-forming antenna, and at least one radio network controller (RNC). The antenna is capable of beam-forming and beams emanating from the antenna may be adjusted in accordance with actual conditions in the wireless communication system. The antenna is further capable of dithering beams in the azimuth and/or elevation plane for breaking up null areas due to beam overlap.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/656,495, filed on Sep. 5, 2003, and claims priority fromU.S. Provisional Application No. 60/409,972, filed on Sep. 9, 2002, bothof which are incorporated herein by reference as if fully set forth.

FIELD OF INVENTION

This invention generally relates to beam-forming in wirelesscommunications, and more particularly to improved beam-formingtechniques so as to achieve an improved signal to noise (S/N) ratiobetween wireless transmit/receive units (WTRUs) and Node Bs in bothuplink and downlink transmissions.

BACKGROUND

Wireless communication systems are well known in the art. A typicalwireless communication system in accordance with current 3GPPspecifications is depicted in FIG. 1. By way of example, the networkarchitecture shown in FIG. 1 is that of UMTS. The UMTS networkarchitecture includes a Core Network (CN) interconnected with a UMTSTerrestrial Radio Access Network (UTRAN) via an interface known as Iuwhich is defined in detail in the current publicly available 3GPPspecification documents. The UTRAN is configured to provide wirelesstelecommunication services to users through wireless transmit/receiveunits (WTRUs), known as User Equipments (UEs) in 3GPP, via a radiointerface known as Uu. The UTRAN has one or more Radio NetworkControllers (RNCs) and base stations, known as Node Bs in 3GPP, whichcollectively provide for the geographic coverage for wirelesscommunications with WTRUs. One or more Node Bs are connected to each RNCvia an interface known as Iub in 3GPP. The UTRAN may have several groupsof Node Bs connected to different RNCs, two are shown in the exampledepicted in FIG. 1. Where more than one RNC is provided in a UTRAN,inter-RNC communication is performed via an Iur interface.Communications external to the network components are performed by theNode Bs on a user level via the Uu interface and the CN on a networklevel via various CN connections to external systems.

In general, the primary function of Node Bs is to provide a radioconnection between the Node Bs' network and the WTRUs. Typically a NodeB emits common channel signals allowing non-connected WTRUs to becomesynchronized with the Node B's timing. In 3GPP, a Node B performs thephysical radio connection with the WTRUs. The Node B receives signalsover the Iub interface from the RNC that control the radio signalstransmitted by the Node B over the Uu interface.

A CN is responsible for routing information to its correct destination.For example, the CN may route voice traffic from a WTRU that is receivedby the UMTS via one of the Node Bs to a public switched telephonenetwork (PSTN) or packet data destined for the Internet. In 3GPP, the CNhas six major components: 1) a serving General Packet Radio Service(GPRS) support node; 2) a gateway GPRS support node; 3) a bordergateway; 4) a visitor location register; 5) a mobile services switchingcenter; and 6) a gateway mobile services switching center. The servingGPRS support node provides access to packet switched domains, such asthe Internet. The gateway GPRS support node is a gateway node forconnections to other networks. All data traffic going to otheroperator's networks or the internet goes through the gateway GPRSsupport node. The border gateway acts as a firewall to prevent attacksby intruders outside the network on subscribers within the networkrealm. The visitor location register is a current serving networks‘copy’ of subscriber data needed to provide services. This informationinitially comes from a database which administers mobile subscribers.The mobile services switching center is in charge of ‘circuit switched’connections from UMTS terminals to the network. The gateway mobileservices switching center implements routing functions required based oncurrent location of subscribers. The gateway mobile services alsoreceives and administers connection requests from subscribers fromexternal networks.

The RNCs generally control internal functions of the UTRAN. The RNCsalso provide intermediary services for communications having a localcomponent via a Uu interface connection with a Node B and an externalservice component via a connection between the CN and an externalsystem, for example overseas calls made from a WTRU in a domestic UMTS.

Typically, an RNC oversees multiple Node Bs, manages radio resourceswithin the geographic area of wireless radio service coverage servicedby the Node Bs, and controls the physical radio resources for the Uuinterface. In 3GPP, the Iu interface of an RNC provides two connectionsto the CN: one to a packet switched domain and the other to a circuitswitched domain. Other important functions of the RNCs includeconfidentiality and integrity protection.

An RNC has several logical roles depending on the CN's needs. Generally,these functions are divided into two components: a serving RNC (S-RNC)and a controlling RNC (C-RNC). As a serving RNC (S-RNC), the RNCfunctions as a bridge to the CN and the Node Bs. As a controlling RNC(C-RNC), the RNC is responsible for the configuration of a Node B'shardware. The C-RNC also controls data transfers and handles congestionbetween different Node Bs. A third logical role of an RNC is as aDrift-RNC. As a Drift-RNC, the RNC is responsible for handing off theWTRU to another Node B as the WTRU traverses the coverage area.

The RNCs and the Node Bs together perform radio resource management(RRM) operations, such as “inner loop power control.” This is a featureto prevent near-far problems. Generally, for example, if several WRTUstransmit at the same power level, the WRTUs closest to a Node B maydrown the signals from the WRTUs that are farther away. The Node Bchecks the power received from the different WRTUs and transmitscommands to the WRTUs to reduce or increase power until the Node Breceives the power from each WRTU at about the same level.

Conventionally, a Node B will provide wireless communication for manyWTRUs. Node Bs will typically handle multiple communications withsubscriber systems concurrently. One measure of Node B capacity is themaximum number of concurrent communications it can support which is afactor determined by such things as available power and bandwidth.

Since not all subscribers communicate with the Node B at the same time,a Node B can provide wireless service to a great many subscribers beyondits capacity for concurrent communications. If the maximum number ofconcurrent communications for a Node B is being conducted, an attempt toestablish a further communication will result in an indication ofservice unavailability, such as a system busy signal.

Service coverage by a Node B is not only limited to its capacity forhandling concurrent communications, but is also inherently limited to aspecific geographic area. A Node B's geographic range is typicallydefined by the location of the Node B's antenna system and the power ofthe signal broadcast by the Node B.

In order to provide wireless service over an expansive geographic area,a network system is conventionally provided with multiple Node Bs. EachNode B has its antenna system selectively physically located to providecoverage over a specific portion of the total geographic area which iscovered by the system. Such systems readily provide wireless service forWTRUs which can travel out of the range of one Node B and into the rangeof another Node B without interruption of an ongoing wirelesscommunication. In such networks, the geographic area covered by a Node Bis commonly referred to as a cell and the telephone communicationservices provided are commonly called cellular telephone services.

In designing a wireless communication system to cover a specificgeographic area, the geographic area may be partitioned into apredefined pattern of cells. For example as illustrated in FIG. 2A,hexagonal-shape cells can be defined so that the cells cover the entiregeographic area in a honeycomb pattern. In such a system, each cell canhave a Node B which has an antenna at the center of the cell to provide360° coverage. Although a map of cell coverage may be designed withoutany overlapping areas, in practice as shown in FIG. 2B, the transmissionbeams, shown in phantom, from Node B antennas of adjacent cells dooverlap. This overlap of beam coverage enables “handover” of acommunication being conducted by a WTRU from one Node B to another asthe WTRU travels from one cell to another. However, an overlapping NodeB signal contributes to interference of a signal received by a WTRU froma different Node B when the WTRU is located in the overlap area.

To more readily meet service demands and reduce interference,beam-forming may be used. Beam-forming in communications is a veryuseful tool, and is implemented by using an array of antennas fortransmission, reception or both, in such a manner that will best matchthe channel requirements. The phase and amplitude of the signals in eachantenna are precisely controlled so as to obtain a constructive patternat the receiver.

Known methods of beam-forming have addressed adjustment of the beams inthe horizontal direction. Additionally, in prior art, transmission-poweradjustment or deployment of wide vertical beams for receiving signalshave been used to match the channel requirements. This technique helpsto cope with severe multipath situations and overcomes extra attenuationby providing extra effective power concentration. Beam-forming has alsobeen utilized in handling interference from other transmission sources.

Although beam forming provides many benefits, present implementationscause various issues that need to be addressed. By way of example,present implementations of beam-forming suffer from the beams intrudingon adjoining cells. The intrusion can be to/from a neighboring cell andis sometimes especially pronounced if the beam-forming includes a broadvertical beam component to reach WTRUs. Furthermore, objects, terrain,etc. also interfere with the vertical component of wide beams.

It is therefore desirable to obviate the disadvantages encountered inknown implementations of beam-forming.

SUMMARY

The present invention is a wireless communication system fortransmitting and receiving wireless communications using at least onebeam. The system comprises a plurality of WTRUs, at least onebeam-forming antenna, and at least one radio network controller (RNC).The antenna is capable of beam-forming and beams emanating from theantenna may be adjusted in accordance with actual conditions in thewireless communication system. The antenna is further capable ofdithering beams in the azimuth and/or elevation plane for breaking upnull areas due to beam overlap.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description of a preferred embodiment, given by way of exampleand to be understood in conjunction with the accompanying drawingswherein:

FIG. 1 is a wireless communication system in accordance with current3GPP specifications;

FIG. 2A is a geographic coverage area of a telecommunication systemwherein the geographic area is partitioned into a predefined pattern ofhexagonal-shape cells;

FIG. 2B is a geographic coverage area of a telecommunication systemwherein the transmission and/or receiver beams of adjacent cellsoverlap;

FIG. 3 is a conventional wireless communication system wherein a beam isbeing transmitted and/or received from a Node B to a plurality of WTRUs;

FIG. 4 is a wireless communication system wherein a beam may bedynamically adjusted in at least a vertical dimension in accordance withthe present invention;

FIG. 5 is a beam being dynamically adjusted in a vertical dimension toaccommodate changes in elevation of WTRUs;

FIG. 6 is a schematic illustration of two transmission beams thatoverlap in at least a vertical dimension having null areas therein;

FIG. 7 is a schematic illustration of two transmission beams beingdithered in at least a vertical dimension to break up null areas;

FIG. 8 is a beam being dynamically adjusted in at least a verticaldimension to provide spatial multiplexing;

FIG. 9 is a beam being dynamically adjusted in at least a verticaldimension to provide spatial and time diversity;

FIG. 10 is a pair of beams being dynamically adjusted in at least avertical dimension at the same time to provide spatial layering;

FIG. 11 is a schematic illustration of multiple transmission beamsemanating from a single antenna having null areas in overlapping regionsof the multiple beams;

FIG. 12 is a schematic illustration of multiple transmission beamsemanating from a single antenna reflecting off of an obstruction andhaving a null area in the overlapping regions of the reflected beams;and

FIG. 13 is a schematic illustration of multiple transmission beamsemanating from a single antenna being dithered in at least a horizontaldimension to break up null areas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention will be describedwith reference to the drawing figures wherein like numerals representlike elements throughout.

Hereafter, a wireless transmit/receive unit (WTRU) includes but is notlimited to a user equipment (UE), mobile station, fixed or mobilesubscriber unit, pager, or any other type of device capable of operatingin a wireless environment. Each of these terms may be usedinterchangeably herein. When referred to hereafter, a Node B includesbut is not limited to a base station, site controller, access point orany other type of interfacing device in a wireless environment. Each ofthese terms may be used interchangeably herein. The terms antenna andantenna array may also be used interchangeably herein to refer to anantenna capable of beam forming.

Referring initially to FIG. 3, there is shown a prior art system whereina beam 10 is directed from an antenna 12 towards a plurality of WTRUs14. The energy of the beam 10 does not stop at the contour shown, butactually extends further out with decreasing power density. Therefore,even with a beam-forming antenna 12, the beam 10 still encompasses theneighboring cell thereby causing interference to a neighboring antenna16. That is, when the beam 10 is a transmit beam, antenna 16 willreceive interference from antenna 12. Similarly, when the beam 10 is areceive beam, any transmission from antenna 16 contributes to the noiseseen by antenna 12.

Referring now to FIG. 4, a system 100 according to the present inventionis shown. In the system 100, a beam 10 is dynamically tilted downwardapproximately as shown. By dynamically tilting the beam 10 downward, thebeam 10 is not directed towards the neighboring antenna 16 as in FIG. 3,but still encompasses the WTRUs 14 with a contour that is adequate forcommunication. Dynamically tilting the beam 10 downward will notcompletely eliminate interference from or to antenna 16, but willgreatly reduce it. In many cases, the down tilt will actually direct thebeam 10 into the surrounding surface after it encompasses the WTRUs 14.With respect to transmission, this means that a fraction of the energyof a beam will often be absorbed by the surface, and another fractionwill be scattered from the original directional path. The overall effectof this is that the energy at any point past the impact area is a lotless than if the beam had propagated past that point in free air. Withrespect to reception, this means that the extended beam volume of spacewill be mostly receiving from a very low source of noise.

System 100 includes at least one radio network controller (RNC) 18, atleast one Node B 20, at least one beam forming antenna 12, and aplurality of WTRUs 14. The effective height of antenna 12 may be anyheight, as desired. Furthermore, the effective height of the antenna 12may be defined according to operator preference, again as desired. Forexample, in one embodiment, the effective height of antenna 12 ispreferably at least twenty (20) feet wherein the effective height isdefined as the height of the antenna 12 above sea level minus theaverage level of ground within a predetermined geographical areaencompassing the antenna 12.

The determination of when to tilt and the computation of the desiredtilt information may be done at the RNC 18 or Node B 20, but ispreferably performed at the RNC 18. It is preferable to perform thesefunctions at the RNC 18 because the RNC 18 has knowledge regarding allof the Node Bs it is responsible for controlling. The RNC 18 cantherefore determine when to tilt and, if appropriate, compute desiredtilt information dynamically (i.e. in real time) based on, at least inpart, the affect tilting a particular beam 10 may have on antenna 12and/or other antennas controlled by the RNC 18. This also enables notonly information from the RNC 18, but also information from WTRUs 14 tobe used when computing tilt information. The determination of when totilt is based on operator preference. By way of example, thedetermination of when to tilt may be based on channel usage, capacitypower levels, distances between cell sites and WTRUs, devicesensitivities, the ability or lack thereof of adjacent cell sites totilt beams, and other sources of interference which the network has noknowledge and/or control over.

Performing the determination of when to tilt and the computation of thedesired tilt information at the RNC 18 or Node B 20 depends on, at leastin part, timing considerations. That is, if the reaction time betweenissuance of tilt information and actual tilting of a beam is measured inless than a few tenths of a second, the determination and computationshould typically be done at the Node B 20. To allow for reactiondiscrepancies between issuance of tilt information at the RNC 18 andNode B 20, a preferred embodiment is to allocate general resources andadjustment limits at the RNC 18 in a slow mode, leaving the Node B 20free to allocate and adjust the beam 10 in a fast mode within the limitsset by the RNC 18. This type of arrangement is currently used withrespect to frequency allocation wherein an RNC allocates availablefrequencies to each Node B controlled by the RNC. The Node Bs are thenfree to utilize their allocated frequencies as they deem best, subjectto any reallocations performed by the RNC based on the RNC's overallview of the Node Bs under its control.

An example of desired tilt information provided by an RNC 18 to a Node B20 in accordance with the preferred embodiment may be as follows. Boreaxis Horizontal between 15 and 40 degrees North; bore axis Verticalbetween 15 degrees above and 30 degrees below horizontal; beam widthbetween 180 and 20 degrees; and power between 0 and −30 dB.Alternatively, some of the limits may be algorithmically derived basedon other constraints. For example, the power limit provided by an RNC 18may be calculated as a function of vertical beam width, horizontal beamwidth, vertical beam bore angle, distance between transmitter andreceiver, and reported received power.

The circuitry for controlling the tilting of a beam 10 in accordancewith the desired tilt information may be located in close proximity tothe antenna 12 or some distance away. Where the tilt-control circuitryis located in close proximity to the antenna 12, the desired tiltinformation may be sent directly to the local circuitry of the antenna12. Where the tilt-control circuitry is remotely located at the Node B20, for example, the desired tilt information is sent to the Node B 20wherein signals for adjusting the beam 10 according to the desired tiltinformation are generated and transmitted to antenna 12.

Whether the control circuitry is located locally or remotely withrespect to antenna 12 is a tradeoff of many factors and is based purelyon operator preference. For example, sending the desired tiltinformation directly to the local circuitry of the antenna 12 allows thecontrol signals to be locally generated, which tend to be more preciseand faster acting. This arrangement is harder to maintain, however,since access to the top of the tower 13 is required every time physicalaccess to the local circuitry is required. Where the control circuitryis remotely located with respect to the antenna 12 (e.g. at the Node B),the circuitry is easier to access, but requires means for transmittingappropriate control signals between the Node B 20 and the antenna 12.For example, multiple cables or a single cable as well as multiplexingencoding and decoding circuitry may be provided.

The actual adjustment of a beam in the vertical dimension is done byadjusting the beam's boresight. The beam boresight may be adjusted bymechanical means, electronic/electrical means, or a combination thereof.A beam's boresight may be adjusted mechanically by adjusting thephysical radiating elements, reflectors, or parasitic elements of anantenna 12, as understood by those skilled in the art. A beam'sboresight may be adjusted electronically by adjusting the phase andamplitude of signals emanating from an antenna 12, as also understood bythose skilled in the art.

As mentioned above, a combination of mechanical and electronic/electricboresight adjusting may be utilized as desired. For example, mechanicaladjustment may be used for large scale coarse usage andelectronic/electrical adjustment for smaller scale finer adjustments. Itis also possible that one type of adjustment is performed in thehorizontal dimension and another in the vertical dimension. The type ofadjustment utilized to adjust the beam 10 in accordance with the desiredtilt information provided by the RNC 18 or Node B 20 is based onoperator preference. Regardless of the type of adjustment that is used,appropriate control signals for implementing the desired tiltinformation are sent to the antenna 12 so that the boresight of the beamis adjusted in accordance with the tilt information generated at the RNC18 or Node B 20. It is important to note, therefore, that althoughmechanical means are shown in FIGS. 4, 6, and 7 andelectronic/electrical means are shown in FIGS. 5, 8, 9, and 10, this ispurely for purposes of describing the invention as either mechanical,electronic/electrical or a combination thereof may be used in anyimplementation of the present invention.

Dynamically tilting a beam 10 in a vertical direction allows the beam 10to be made narrower in the vertical dimension, as can be seen bycomparing beam 10 in FIGS. 3 and 4. The beam narrowing is done byadjusting the phase and magnitude emanating from an antenna array in thevertical dimension.

A beam that is narrower in the vertical dimension results in additionalnoise benefits in the transmit and receive operations. That is, as withthe horizontal dimension, any restriction of the beam in the verticalspace is beneficial with respect to transmission and reception. Withrespect to receivers, a smaller beam means less receivers will besubject to interference emanating from the beam. With respect totransmitters, a smaller beam means lower transmission power is necessaryto achieve the same power density in the region of the intendedreceiver. A smaller beam also results in fewer multipaths occurring interrains that are prone to multipath.

It should be noted that in some circumstances it is actually desirableto receive multiple multipaths from the same source (i.e. where thereduction of multipath is not a desirable result). Such cases are, forexample, when the power level necessary to decode the signal isinsufficient from one path, and/or the multipath provides an improvementin signal robustness because not all of the paths are simultaneouslydisturbed by signal fading. This utilization is often referred to asspatial diversity transmission when purposely performed at transmitters,and spatial diversity reception when purposely performed at receivers.It should further be noted that beamforming can still be useful in thesecases by monitoring the several most significant paths and eitherswitching between or combining them for decoding. This can be done bygenerating multiple receive beams or widening a single beam to interceptthe multipath beams.

Referring now to FIG. 5, another utilization of dynamic vertical beamforming is shown. In this embodiment, beams may be adjusted up or downto compensate for differences in the elevation of WTRUs. By verticallyadjusting the beam, the communication link with the target (receiving ortransmitting) can be made more robust, and with less interference withother devices.

By way of example, when a WTRU 40 is at a high elevation with respect toan antenna 42, a beam 44 may be dynamically tilted upward so that thebeam's contour is directed toward the WTRU 40. Similarly, when a WTRU 46is at an elevation that is lower than that of the antenna 42, the beam44 may be dynamically tilted downward.

Referring now to FIGS. 6 and 7, another embodiment of the presentinvention is to utilize dynamic tilting of beams to dither beams (i.e.dithering) in the vertical dimension so as to break up null areas. InFIG. 6, portions of normalized power patterns from two antennas 112, 114(i.e. plural transmitters) are shown. In this embodiment, the twoantennas 112, 114 belong to separate Node Bs and are transmittingsignals, represented by radiation beam patterns 116, 118, with anoverlap region 120 of their beams. It is understood that the depictedpatterns are of a given field signal intensity and are not nearly assharply defined as depicted. The majority of the interference betweenthe beams (overlapping region 120) does not lead to a WTRU in the areabeing unable to receive the signal in a decodable fashion. If the timingis correct and the error-correcting capability of the codes used in thedata streams is robust enough, the WTRUs in most if not all of anoverlapping region will be able to decode the transmission. Areas 122,124, however, are places where the interference does not allow robustdecoding (i.e. null areas).

The significant aspect of this situation is that some WTRUs may be inpositions, such as 122 and 124, where the interference of the signalsdoes not allow decoding of the transmission. Depending on the nature ofthe transmission, some WTRUs would just miss the signal. Others wouldinterrogate the system later to see if they had missed some message, andif so request its retransmission uniquely to them.

FIG. 7 shows the effect of the two signals 116, 118 being dithered in avertical dimension. Note, however, that a single beam or, whereadditional beams are present, any number of beams may be dithered, asdesired. Dithering the beams 116, 118 in the vertical dimension has theeffect of moving the nulls 122, 124 around within area 126. A WTRUwithin a null area 122, 124 would therefore not statically remain withinthe null area 122, 124. Instead, the instantaneous nulls 122, 124 arenow being moved over a larger physical area 126, but with a lowerduration. It is important to note that, as discussed above, a signal maybe dithered electronically/electrically using boresight control,amplitude control, or a combination of amplitude control and boresightcontrol.

It should be noted that null areas may also occur not because of signalsemanating from two separate antennas, but from a single antenna whosesignal is subject to multipath. That is, in the case of multipath, oneor more of the multipath signals may overlap the original signal therebycausing null areas within an overlapping region. In this situation, thebeam may dithered in the vertical direction to move the null areasaround to reduce the likelihood that WTRUs remain within a null area fora period of time that is sufficient to affect transmission.

Referring now to FIG. 8, another embodiment of the present invention isto dynamically adjust beams in a vertical dimension to achieve spatialmultiplexing. Spatial multiplexing is the transmission of multipledifferent signals sent along multiple different paths to multipledifferent WTRUs. For example, in FIG. 8, antenna 142 is transmittingmultiple signals 148, 144 each having their own path. Signal 148 istransmitted to WTRU(s) 140 and signal 144 is transmitted to WTRUs 146.In this embodiment, the beams are preferably narrowly tailored so as toreduce the amount of interference caused by signal 148 to signal 144,and vice versa.

Referring now to FIG. 9, another embodiment of the present invention isto dynamically adjust beams in a vertical dimension to achieve spatialdiversity. Spatial diversity is the transmission of a single signal sentover multiple different paths to the same WTRU or group of WTRUs in aparticular area. For example, if a building structure 165 is located infront of WTRU 166 that is high enough to block path 164, but not path168, WTRU 166 can still receive the signal from a reflection 170 of path168 or of some other path, as the signal may be sent along any number ofpaths as desired. The greater number of paths on which the signal istransmitted, the greater the odds that a reflected signal will reach thereceiving WTRU(s) 166. Spatial diversity may be performed with two ormore beams transmitted in the same time frame, or in different timeframes as desired. The former is a more efficient utilization of the RFresource in time, but requires more equipment. Which is used istherefore a tradeoff of cost versus system capacity.

Referring now to FIG. 10, another embodiment of the present invention isto dynamically adjust beams in a vertical dimension to achieve spatiallayering. Spatial layering is the transmission of multiple differentsignals directed via reflection or refraction (e.g. around corners) to asingle geographical location so that WTRU(s) capable of decodingmultiple transmissions within that geographical area may receive thesignals at a higher data rate than if the date were sent in a singlesignal. For example, if WTRU 166 is receiving a large transmission, thedata contained in that transmission can be broken down into one or moresignals 168, 164, as desired. In this case, one signal 164 may bedirected directly toward the geographical area in which WTRU 166 islocated, but any number of additional signals 168 may be transmitted sothat their reflected signal(s) 170 reach that same area. This greatlyincreases the data rate at which WTRU 166 can receive the transmission.

It should be noted that dynamic vertical tilting of antennas and beamsas described herein may be implemented alone or in conjunction withhorizontal adjustments of antennas and beams. Furthermore, verticaltilting as described herein may be performed, for example, with switchedbeams (i.e. beams having a finite number of positions) and adaptivebeams (i.e. beams wherein the boresight of the beam is continuouslyupdated to be in an optimal position as determined by the RNC).

Referring now to FIG. 11, another embodiment of the present invention isto dither multiple beams in a horizontal dimension. Antenna 200 emanatesseveral beams 210 ₁, 210 ₂, 210 ₃, and 210 ₄. The total number ofantenna beams emanating from antenna 200 can be any number of beams asdesired. It should be understood that the depicted patterns are of agiven field signal intensity and are not nearly as sharply defined asdepicted. The overlap of beams 210 ₁ and 210 ₂ create a null area 220 ₁.Similarly, beams 210 ₂ and 210 ₃ yield a null area 220 ₂, and beams 210₃ and 210 ₄ yield a null area 220 ₃. Prior art methods of reducing nullareas caused by beam pattern overlapping utilize methods of polarizationand/or time delay in the beam transmissions. These solutions areinadequate because they may cause a destructive phase relationship amongthe various signals, or the reflections may alter the polarization ofthe signal such that it is no longer orthogonal to the polarization ofthe interfering signal.

Dithering the beams 210 ₁, 210 ₂, 210 ₃, and 210 ₄ in the horizontaldimension has the effect of continuously moving the null area 220 ₁, 220₂, and 220 ₃. A WTRU within the null area 220 ₁, for example, wouldtherefore not statically remain within the null area 220 ₁. Instead, aninstantaneous null area created by overlapping beams is moved over alarger geographic area, but has a shorter temporal duration. A WTRUpositioned in an instantaneous null area utilizing sufficiently robusterror checking codes will be able to decode transmissions from theantenna 200.

Referring now to FIG. 12, in another embodiment of the present inventionan obstruction reflects beam 210 ₃, creating reflection 230 ₃. It shouldbe understood that during reflections, refractions, and propagationsthrough some obstacles, the patterns may become very irregular andnumerous, and for simplicity only a main beam reflection is shown. Thereflection 230 ₃ overlaps beam 210 ₄ creating null area 240. Similar tothe previous embodiment, prior art methods for reducing the null area240 caused by a reflected beam utilize methods of polarization and/ortime delay in the beam transmissions.

Referring to FIG. 13, dithering beam 210 ₃, and consequently beamreflection 230 ₃, and beam 210 ₄, has the effect of continuously movingthe null area 240 over a large geographic area, in turn maintaining ashort temporal duration of the null area 240. A WTRU positioned in anull area 240 utilizing sufficiently robust error checking codes will beable to decode transmissions from the antenna 200.

Dithering as used herein is the technique of continuous, automatic,slight variations in a beam transmission. Beams may be dithered, forexample, in time, carrier frequency, bore sight in the azimuth plane,bore sight in the elevation plane, power, and/or changes in the patterncontour. The dithering may be accomplished by adjusting any of theforegoing beam parameters to any degree and in any combination. Oncedithering is started, it typically continues until the network operatorterminates it. The RNC preferably controls the dithering of variousbeams.

It should be noted that dynamic vertical dithering of antennas and beamsas described herein may be implemented alone or in conjunction withhorizontal dithering of antennas and beams. The combination of verticaland horizontal dithering in effect creates three dimensional dithering.Furthermore, vertical dithering as described herein may be performed,for example, with switched beams (i.e. beams having a finite number ofpositions) and adaptive beams (i.e. beams wherein the boresight of thebeam is continuously updated to be in an optimal position as determinedby the RNC). Dithering may also be used to eliminate null areas createdby overlapping beam patterns from two different antennas.

Although the preferred embodiments are described in conjunction with athird generation partnership program (3GPP) system, the embodiments areapplicable to any wireless communication system utilizing beam forming.

While the present invention has been described in terms of the preferredembodiment, other variations that are within the scope of the inventionas outlined in the claims will be apparent to those skilled in the art.

1. A wireless communication system for transmitting and receivingwireless communications using at least two beams comprising; a pluralityof WTRUs; at least one beam forming antenna wherein at least two beamsemanating from the beam forming antenna overlap creating at least onenull area, and wherein at least one beam is dithered in at least ahorizontal dimension by adjusting at least one beam parameter; and aradio network controller for controlling the dithering of at least oneof the two beams to optimize transmission between the antenna and atleast one WTRU.
 2. The wireless communication system of claim 1 whereinat least one of beam is dithered in a vertical dimension.
 3. Thewireless communication system of claim 1 wherein the beam dithered inthe horizontal dimension is also dithered in a vertical dimension. 4.The wireless communication system of claim 2 wherein a Node B isprovided for generating control signals for dithering the beam inaccordance with tilt information provided by the radio networkcontroller.
 5. The wireless communication system of claim 2 wherein tiltinformation is sent from the radio network controller to the antennawherein control signals are generated for dithering the beam inaccordance with tilt information provided by the radio networkcontroller.
 6. The wireless communication system of claim 1 wherein thebeam is tilted downward to reduce interference to and from anotherantenna.
 7. The wireless communication system of claim 1 wherein thebeam is dithered to account for variations in elevation between theWTRUs.
 8. The wireless communication system of claim 1 wherein the beamis dithered to break up null areas wherein transmission signals are notdecodable.
 9. The wireless communication system of claim 2 wherein thebeam is dithered to break up null areas wherein transmission signals arenot decodable.
 10. The wireless communication system of claim 1 whereinthe dithered beam parameter is time.
 11. The wireless communicationsystem of claim 1 wherein the dithered beam parameter is carrierfrequency.
 12. The wireless communication system of claim 1 wherein thedithered beam parameter is bore sight in the azimuth plane.
 13. Thewireless communication system of claim 1 wherein the dithered beamparameter is bore sight in the elevation plane.
 14. The wirelesscommunication system of claim 1 wherein the dithered beam parameter ispower.
 15. The wireless communication system of claim 1 wherein thedithered beam parameter is pattern contour.
 16. A wireless communicationsystem for transmitting and receiving wireless communications using atleast one beam comprising: a plurality of WTRUs; a radio networkcontroller; at least one beam forming antenna emanating multiple beams,wherein at least one beam emanating from the beam forming antenna isdithered in at least a horizontal dimension; and a Node B forcontrolling the dithering of the beam to optimize transmission betweenthe antenna and at least one WTRU.
 17. The wireless communication systemof claim 16 wherein at least one beam emanating from the beam formingantenna is dithered in a vertical dimension.
 18. The wirelesscommunication system of claim 16 wherein the at least one beam ditheredin a horizontal dimension is also dithered in a vertical dimension. 19.The wireless communication system of claim 16 wherein at least one beamis dithered to break up null areas wherein transmission signals are notdecodable.